This section provides background information related to the present disclosure which is not necessarily prior art.
Currently, in the field of Thin Film Transistor-Liquid Crystal Display (TFT-LCD), in one way, a degree of firmness of a boom may usually be detected by an inspector at an upper interlayer of an OHCV, so as to detect whether or not the OHCV is at a horizontal level or has been sunken. At this time, the inspector may be at an intensive workload and may not find the fault. In addition, due to the frequent inspection, hermeticity of a Fan Filter Unit (FFU) filter at a top of the OHCV will be adversely affected, resulting in leakage at the FFU. Further, in another way, the inspector may enter an interior of the OHCV so as to measure a level degree of he OHCV by a laser level meter. However, at this time, a normal operation of the OHCV well as the cleanliness thereof will be adversely affected.